On a mountain the temperature decreases by 6.5 for every 1000 meters increase in height. At 2000 meters the temperature is 10. Find the temperature at 6000 meters

Astudent must have an average on five test that is greater than it equal to 80% but less than 90% to receive a final grade of b. devon's greades on the first four test were 78% 62% 91% and 80% what range if grades on the fifth test would give him a b in the course? ( assuming the highest grade is 100%)